The present invention relates to magnetically driven centrifugal fluid pumps and particularly to pumps of the sort that have no rotating axle or bearings that penetrate a wall of the pump housing and so the housing is completely sealed against any leakage of the fluid that is pumped and there is no requirement of seals against leakage of the fluid at any moving or rotating part of the pump.
Heretofore, magnetically driven centrifugal pumps that are completely sealed up and have no drive shaft or bearing opening through any wall of the housing of the pump have been provided. Such pumps are often specified where, for any number of reasons, no fluid leakage from the pump can be tolerated. For example: the fluid may be very contaminating; or it may be poisonous or radioactive; or it may simply be a cooling fluid in a closed system that cannot tolerate any leaks. For any of these reasons, magnetically driven pumps have been provided in which the drive to the rotor of the pump is by magnetic coupling through a wall of the pump housing and so there need not be any drive shaft or bearing that penetrate the wall of the pump housing.
The usual form of magnetically driven pumps is the axial magnetic drive pump, which has a rotor within the sealed housing on an axle that is attached to the back inside wall of the housing. The rotor carries several axially oriented magnets behind the impellers and extending from behind the impellers face at the front of the rotor to the back of the rotor. Hence, the back of the rotor is an elongated cylinder that contains several axial magnets arranged regularly around and parallel to the rotor axis of rotation; and the impellers are contained in a disc of substantially larger diameter than the elongated cylinder. A housing encloses the rotor and has the same shape so that the axial magnets of the rotor are close to the inside wall of the housing. The external drive magnetic encloses the elongated cylinder of the housing and is, essentially, a thick walled cylinder containing axially oriented magnets in the thick wall. Thus, the external drive and the rotor axial magnets are concentric. The fields of the external drive axial magnets and the rotor axial magnets couple through the walls of the elongated cylindrical part of the housing and so the direction of the coupling magnetic fields through the housing wall is essentially radial.
The fluid input of such a pump is along the axis and may be into an annular input chamber at the front inside of the housing and from that chamber into rotating radial passages that are partly defined by the impellers attached to the rotor. The fluid is trapped in these rotating radial passages between the impellers and the immediately adjacent front inside wall of the housing and is compelled to flow radially into a peripheral annular output chamber within the housing. Clearly, the pressure of fluid at the input chamber is the input pressure and the pressure at the peripheral annular chamber is the output pressure and the effect of the rotation is to increase the output pressure over the input pressure even while there is a continuous flow of fluid into the input and out of the output. Such pumps are rated by the relationship of flow volume to pressure head. As the flow volume increases the pressure head decreases (maximum pressure head is achieved at zero flow).
Clearly, the axial magnet orientation requires a rotor with an elongated axial part for containing the axial magnets and the axle for such a rotor may have to be supported at both ends. It is difficult to carry such a rotor on an axle that is supported at only one end (cantilevered from one end of the inside of the housing). However, the cantilevered axle is preferred so that the front face of the rotor that carries the impellers has no axle between it and the opposite wall (front inside wall) of the housing as this allows a fluid input along the axis of rotation directly into the center of the impeller face of the rotor. The present invention incorporates a different orientation of the rotor and drive magnets to substantially reduce the axial dimension of the rotor so that it can be easily supported by an axle at the back inside face of the housing and needs no axial support at the front inside face of the housing.
For such pumps where the impeller blades are on the front face of the rotor, the radial fluid passages are between the blades and each passage is defined by adjacent blades, the face of the rotor and the immediately opposite front inside wall of the housing; and there is clearance between the impellers and the housing so that the impellers do not scrape or touch the housing. Since the stationary housing wall is a part of each radial passage, there is a great deal of friction on the fluid where it contacts the front inside housing wall as the fluid is caught by the impellers and rotated so that it flows rotationally and outward from the axial input to the peripheral output. This friction results only in heating the fluid and is to be avoided. The embodiment of the present invention also incorporates another improvement to a centrifugal pump of this sort, that tends to reduce the forces of friction on the fluid as it flows radially as it is driven by the impellers from the axial input to the peripheral output.